1. Field of the Invention
An aspect of the present invention relates to a distribution of security keys among nodes of a wireless network. More particularly, an aspect of the present invention proposes a scheme aiming to reduce a number of security keys for storages in each node.
2. Description of the Related Art
Nodes of a wireless network set security keys to protect data from a malicious third party during transmission and reception of the data. In other words, each node encrypts data using set security keys and then transmits the encrypted data. Therefore, with the use of these nodes, data may be transmitted and received safely from the harm of the malicious party.
Currently available schemes to set security keys for the nodes of a wireless network, or, more particularly, of an ad-hoc network, will be briefly described below.
First, each node may set a security key using a channel other than a channel to be used for data transmission. In other words, the nodes may set security keys using infrared rays or using lines. In these cases, the nodes are located at a short transmission distance and therefore, intrusion of an unwanted third party may be generally avoided. However, such a short transmission distance also works as a disadvantage because the coverage of nodes setting security keys is limited to only within a short distance.
The nodes may set security keys by a direct contact, or using human body as a channel. In other words, the nodes may set security keys using an electric current flowing in a human body that contacts the node. This scheme, however, provides a restriction that a separate channel needs to be used in addition to channels for communication among the nodes.
Secondly, a sending node and a receiving node may transmit and receive data using a public key. However, in this scheme, a large amount of computations for data encryption or decryption are required.
Meanwhile, RSA is an encryption code which has been developed by Ron Rivest, Adi Shamir and Leonard Adleman. The RSA mainly utilizes the fact that the resolution of large integers into factors is difficult and is currently popular. However, the elliptical curve cryptography and resolution into factors with 514-bits have recently attacked the RSA, and therefore, a larger modulus ‘n’ was used to construct a safer RSA cryptography system. Accordingly, 1024-bit security keys are currently used.
FIG. 1 illustrates nodes constructing a wireless network. According to FIG. 1, a wireless network includes a first node 101, a second node 102, a third node 103, and a fourth node 104. A method to operate these nodes in a conventional wireless network so as to set security keys will now be described. First, all the nodes of a wireless network may allocate identical security keys. Accordingly, the first to fourth nodes 101-104 are allocated with the same security key. That is, when the first node 101 has data to transmit to the second to fourth nodes 102-104, the first node 101 encrypts data using one security key and transmits the encrypted data. By doing so, the number of security keys to be stored in each node may be minimized. In other words, one security key is stored in each of the nodes even when the number of nodes increases in a wireless network. Accordingly, the wireless network also requires one security key.
However, sharing a single security key among the first to fourth nodes 101-104 is accompanied with a security risk because the security key of all nodes is exposed when even one node exposes the security key thereof. Accordingly, a solution to this problem is demanded.
Secondly, nodes of a wireless network may be allocated with different security keys, which is illustrated in FIG. 2. Here, a wireless network allocates first to sixth security keys that are stored in the respective nodes. Namely, the first to third security keys are allocated to the first node 101, and the first, fourth and fifth security keys are allocated to the second node 102. The second, fourth and sixth security keys are allocated to the third node 103, and the third, fifth, and sixth security keys are allocated to the fourth node 104.
The first node 101 uses the first security key to transmit data to the second node 102, uses the second security key to transmit data to the third node 103, and uses the third security key to transmit data to the fourth node 104. The second node 102 uses the first security key to transmit data to the first node 101, uses the fourth security key to transmit data to the third node 103, and uses the fifth security key to transmit data to the fourth node 104. The third node 103 uses the second security key to transmit data to the first node, uses the fourth security key to transmit data to the third node 103, and uses the sixth security key to transmit data to the fourth node 104. The fourth node 104 uses the third security key to transmit data to the first node 101, uses the fifth security key to transmit the data to the second node 102, and uses the sixth security key to transmit data to the third node 103.
By allocating a pair of nodes with their own security keys, all the other security keys may remain hidden even when a certain security key is exposed. However, as the number of nodes increases in a wireless network, the number of security keys to be stored in the nodes also increases, and therefore, the number of security keys required by the wireless network also increases. The following equation 1 shows the number of security keys required to be stored in each node when the number of nodes is ‘N’.
[Equation 1]Number of security keys required to be stored in each node=N−1
The following equation 2 shows the number of security keys required by a wireless network when the number of nodes of the wireless network is ‘N’.
[Equation 1]Number of security keys required in wireless network=(N−1)+(N−2)+ . . . +1
As may be inferred from the equation 1, a number of security keys required to be stored in each node increases when a number of nodes of a wireless network increases. And as inferred from the equation 2, a number of security keys required in a wireless network increases geometrically when a number of nodes of a wireless network increase. Accordingly, a method is required to reduce number of required security keys when the number of wireless network nodes increases.